The present invention relates to an electron gun, a color cathode ray tube and a display apparatus, and more particularly to an inline type electron gun capable of producing a plurality of electron beams from each of cathodes, a color cathode ray tube using such an electron gun, and also to a display apparatus using the same.
As shown in FIG. 1, a conventional electron gun 8 employed in a known color cathode ray tube has three cathodes.
A cathode 1-KR is used for displaying red, a cathode 1-KG for displaying green, and another cathode 1-KB for displaying blue, respectively.
Electrons generated in the individual cathodes are accelerated by grids 2-7 to form three electron beams.
Each of the electron beams is irradiated onto a fluorescent screen of the cathode ray tube.
The electron beams collide with red, green and blue fluorescent materials, and light is generated at the points of such collision.
As shown in FIG. 2, a deflection yoke 9 is attached to the outside of a glass bulb 10 of the cathode ray tube.
Currents of horizontal and vertical deflection periods are caused to flow in the deflection yoke 9 by circuits incorporated in a display apparatus.
The deflection yoke 9 generates magnetic fields in accordance with such currents, so that the electron beams 12 are deflected in both horizontal and vertical directions.
The fluorescent screen 11 of the cathode ray tube are scanned by the electron beams to display an image thereon.
In order to enhance the luminance of the image in the cathode ray tube, it is necessary to increase the current quantity of the electron beams.
According to the related art, it has been customary heretofore that one electron beam is produced from one cathode.
The diameter of an electron beam tends to become greater with an increase of the current quantity.
For this reason, there exists a relationship that the resolution of an image is deteriorated as the luminance thereof becomes higher.
Accordingly, some limitation is unavoidable in raising the luminance while maintaining the resolution to a certain extent.
For the purpose of solving the above problem, an improvement has been contrived to produce a plurality of electron beams per color so as to raise the luminance without inducing deterioration of the resolution. In this case, the plurality of electron beams are irradiated in respective directions slightly different from one another.
In a process of employing two electron beams per color for example, there have been tried a variety of methods inclusive of one that produces six electron beams from six cathodes, or one that produces two electron beams from each of three cathodes.
However, the above method of increasing the number of cathodes to six raises a problem in carrying into effects practically since some difficulties are existent in realizing a dimensional reduction of the electron gun.
Further, any of the known methods mentioned above brings about a problem that it is difficult to attain a positional coincidence between electron beams on the fluorescent screen.
More specifically, the positions where two electron beams per color collide with the fluorescent screen need to be mutually coincident.
And if the positional deviation is great, it causes deterioration of the image resolution.
As obvious from FIG. 2, the distance required for any traveling electron beam to reach the fluorescent screen is different in the central area and the peripheral area of the screen.
That is, the distance of travel required for any electron beam to reach the peripheral area of the fluorescent screen is longer than the distance required for the electron beam to reach the central area of the fluorescent beam.
Therefore, even if the setting is so determined that the positions of collision of two electron beams are mutually coincident in the central area of the fluorescent screen, the two electron beams positionally coincide, in the peripheral area of the fluorescent screen, at points anterior to the fluorescent screen.
Consequently, a positional deviation occurs between the two electrodes in the peripheral area of the fluorescent screen.
As a result, it has been difficult heretofore to attain a positional coincidence between the electron beams on the entire fluorescent screen.
In view of the problems described above, it is an object of the present invention to realize an improved inline type electron gun which produces a plurality of electron beams from each of cathodes and ensures a positional coincidence between the plurality of electron beams over the entire area of a fluorescent screen. Another object of the present invention resides in providing a color cathode ray tube using such an inline type electron gun. And a further object of the present invention is to provide a display apparatus equipped with such a color cathode ray tube using the electron gun of the invention.
According to one aspect of the present invention, there is provided an inline type electron gun comprising three cathodes. In first and second grids of this electron gun, a plurality of beam apertures are formed per cathode. The optimal number of electron beams produced from each cathode is two or three.
The second grid is split into a plurality of grids which are spaced apart mutually in the traveling direction of the electron beams. The optimal number of such split grids is two or three.
The beam apertures in at least one of the split grids are so formed as to be eccentric to the beam apertures in the other split grid.
And a voltage generated by a circuit in the display apparatus and changed synchronously with the deflection period is impressed to at least one of the split grids.
In the first and second grids, a plurality of beam apertures are formed per cathode, and a plurality of electron beams are produced from each of the cathodes.
The second grid is split into a plurality of grids, and the beam apertures in at least one split grid are formed to be eccentric to those in the other split grid.
Consequently, any electron beam passing through the second grid is curved by the field lens effect between the grids.
When the voltage of a waveform synchronized with the deflection of the electron beam is impressed to at least one of the split grids, the field lens effect is changed in accordance with the impressed voltage.
More specifically, the quantity of curvature of the electron beam is changed in conformity with the voltage waveform in the grid.
Normally, the positional deviation between the plural electron beams includes both horizontal and vertical components. In order to correct these two components, a beam aperture having a vertical eccentricity is formed in, for example, one split second grid, while a beam aperture having a horizontal eccentricity is formed in another split second grid. And the voltages of waveforms changed synchronously with the deflection period are impressed to such two split grids independently of each other.
If the waveforms of the voltages impressed to the two split grids are optimized by properly controlling the circuits in a display apparatus, then it becomes possible to attain a positional coincidence in collision of plural electron beams over the entire area of the fluorescent screen.
The above and other features and advantages of the present invention will become apparent from the following description which will be given with reference to the illustrative accompanying drawings.